Octagen's broad, long-term objective is to complete the clinical development and secure FDA approval of its b-domain deleted recombinant factor VIII (OBI-1), a low antigenicity version of factor VIM (fVIII). OBI-1 is designed for the treatment of patients with inhibitory, neutralizing antibodies to human fVIII. Such "inhibitor" patients include congenital hemophiliacs who are refractory to human fVIII, as well as patients with "acquired hemophilia." The development of an inhibitor to human fVIII is a serious, potentially life-threatening condition. Current treatment options are not always effective and there is a need for improved therapies. The specific aims of this application are to conduct: 1. an open-label, non-comparative phase II study of the hemostatic efficacy, pharmacokinetics and safety of OBI-1 in non-life and non-limb-threatening bleeding episodes in congenital hemophilia A inhibitor patients, 2. an open-label, non-comparative phase III study of the efficacy and safety of OBI-1 in long-term repeated treatment of hemorrhages congenital hemophilia A inhibitor patients, 3. an open-label, non-comparative phase III study of the efficacy and safety of OBI-1 in the treatment of hemorrhages in patients with acquired hemophilia A, 4. an open-label, non-comparative phase III study of the efficacy and safety of OBI-1 in prophylaxis during surgery in patients with congenital hemophilia A inhibitor patients, 5. an open-label, non-comparative phase III study of the efficacy and safety of OBI-1 in prophylaxis during surgery in patients with acquired hemophilia A, 6. an open-label, non-comparative phase III study of the efficacy and safety of OBI-1 in the treatment of hemorrhages in hemophilia A inhibitor patients and in acquired hemophilia A patients in whom all approved products have failed to control the hemorrhage.